A typical magnetoresistive spin-valve sensor includes a base layer, a first magnetic (pinned) layer, a spacer layer, and a second magnetic (free) layer which are stacked in this order. By increasing the output of the magnetoresistive spin-valve sensor, it is possible to read information from magnetic recording media having a high recording density.
For example, the use of a highly conductive back layer on the free layer is proposed in a U.S. Pat. No. 5,422,571. By the provision of the back layer, the electron mean-free-path is increased due to the so-called “spin-filter effect”, thereby increasing the output of the magnetoresistive spin-valve sensor.
On the other hand, the use of a specular layer on the free layer is proposed in Egelhoff et al., “Specular electron scattering in metallic thin films”, J. Vac. Sci. Technol. B 17(4), July/August 1999. By the provision of the specular layer, the specularity of conduction electrons is increased, thereby increasing the spin-dependent scattering and the electron mean-free-path. As a result, the output of the magnetoresistive spin-valve sensor is increased.
It is possible to increase the output of the magnetoresistive spin-valve sensor by decreasing the thickness of the free layer because a magnetic flux density and thickness product, that is, a tBs value, decreases accordingly, where t denotes the thickness of the free layer and Bs denotes the magnetic flux density of the free layer. However, it is difficult to decrease the thickness of the free layer while maintaining a small coercive field and a small interlayer coupling field Hin between the pinned layer and the free layer, particularly when the specular layer is in direct contact with the free layer.
Alternatively, it is also possible to increase the output of the magnetoresistive spin-valve sensor by decreasing the thickness of the spacer layer because a shunt current which does not contribute to the magnetoresistive effect decreases accordingly. But it is difficult to decrease the thickness of the spacer layer without increasing the interlayer coupling field Hin between the pinned layer and the free layer.